The invention relates to a method and a device for correcting gaps between mail items.
In the course of processing mail items, such as letters, postcards and the like for example, in larger mail distribution centers, the mail items frequently pass through a number of processing machines, in particular sorting machines, in succession, which machines are connected to one another using transport means. It is often the case here that the upstream machines have a higher throughput than the following ones.
If, for example, an upstream device for address reading, with a processing rate of 4 m/s given an average mail item length of 200 mm and an average gap of 106 mm, has a higher throughput than a following precision distribution machine having a processing rate of 3.2 m/s with a required gap of 70 mm, then the gap would have to be corrected for the precision distribution machine since following the jump in speed only gaps of 45 mm on average are produced. An average of 25 mm is therefore missing per gap. In order to create the required gaps, the mail items must be shifted back. In existing correction devices, this is performed by slowing down the mail items and speeding them up again by means of variable-speed roller pairs.
To attain a gap of 70 mm, the first mail item must be shifted back by 25 mm. A gap of only 20 mm is therefore produced behind this mail item. The second mail item then needs to be shifted back by 50 mm. If the second mail item is again followed by an average gap, then the second mail item would be pushed onto the third mail item. To avoid this, a large gap would have to occur every 3 mail items, that is to say a mail item must be removed from the mail stream. This would greatly reduce throughput however.
The object of the invention is therefore to increase too small gaps in a mail stream in such a way that as few as possible mail items must be removed from the supplied mail stream.
As a minimum requirement here, only as many mail items are ejected from the supplied mail stream as are required to increase the gaps, it being possible to perform said ejection at least partially within an upstream processing process. Mail items are prevented from being pushed on top of one another by dividing the mail stream between two gap-correcting units. Owing to the large spacings between the mail items in the gap-correcting units, the mail items can be shifted to the required extent without the mail items being pushed on to each other prematurely. Both partial streams are subsequently combined into one mail stream, with the gaps between the mail items corresponding to at least the required specified gaps.
It is advantageous to feed back the ejected mail items and reinsert them into the mail stream.